Surface wave preselector

ABSTRACT

A surface wave preselector having a piezoelectric base member upon which is mounted at least one interdigital transmitter grid. The transmitter grid includes a plurality of interdigitated electrodes adapted to receive an electrical input signal and generate a surface wave in the base in response to a selected frequency of the input signal. At least one interdigital receiver grid positioned on the base opposite a transmitter grid and adapted to receive a transmitted surface wave of selected frequency and produce an output signal in response thereto.

United States Patent [191 deKlerk SURFACE WAVE PRESELECTOR Inventor: John deKlerk, Pittsburgh, Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: Apr. 4, 1973 Appl. No.: 347,979

Assignee:

US. Cl 333/72, 310/8.1, 310/98, 333/30 R Int. Cl H03h 9/26, H03h 9/32, l-IOlv 7/00 Field of Search 333/72, 30; 310/8, 8.1, 310/82, 9.7, 9.8

[56] References Cited UNITED STATES PATENTS 6/1971 Adler et al 333/72 X 11/1971 Adler 333/72 12/1971 Knowles 333/72 X 3/1973 Speiser 333/30 10/1973 Whitehouse 333/72 X OTHER PUBLICATIONS Mitchell et al.Surface Wave Filters in Mullard 1 Nov. 5, 1974 Technical Communications, N0. 8, Nov. 1970, Vol. 11; PP- 179-181.

Fisk-Surface Wave Devices in Popular Electronics, March 1971; pp. 29-33.

Primary Examiner-James W. Lawrence Assistant Examiner-Marvin Nussbaum Attorney, Agent, or FirmD. Schron [57] ABSTRACT 4 Claims, 4 Drawing Figures SURFACE WAVE PRESELECTOR FIELD OF THE INVENTION BACKGROUND OF THE INVENTION While known for over a century, elastic surface waves have found practical utility only within the last few years. Of known surface waves, the Rayleigh wave has been the subject of most investigations and has achieved the widest application. The Rayleigh surface wave has a particle displacement which is retrograde elliptical and has both shear and compressional components. One of the most effective methods of generating a Rayleigh wave in a crystalline medium, such as quartz or lithium niobate, is with an electrode structure on the surface of the crystal for electromechanically coupling with the piezoelectric matrix of the crystal. At certain frequencies, phase coherence exists between the acoustic waves generated by individual electrode transducers on the surface. Under such conditions a Rayleigh wave will be generated on the surface and propagate along the surface axis. a

In bulk single crystal piezoelectric materials, such as lithium niobate, silicon dioxide, cadmium sulfide and zinc oxide, delay lines and amplifiers have been fabricated with frequencies up to I MHZ. Surface wave generation, propagation and detection in piezoelectric films, such as cadmium sulfide, zinc oxide, and zinc sulfide, on passive substrates such as M 0 and silicon have also been achieved. These thin films are-capable of being utilized in both dispersive and nondispersive devices between 100 and 400 MHz, depending upon the ratio of the film thickness to the surface wave length.

Surface wave transducers have been successfully utilized in signal processing including radar. An efficient method of generating surface waves is the use of an .interdigital grid on a piezoelectric material. 9 Ultrasonics, p. 35 (I971 Each pair of electrodes of an interdigital grid-generates halfa Rayleigh wavelength. The grid becomes resonant at the frequency for which the spacing between the centers ofadjacent electrodes is half an elastic surface wavelength. When the frequency of the applied alternating voltage is such that the surface acoustic wave coincides with the distance between the centers of two adjacent electrodes of one of the pairs ofgrids, an elastic wave is generated on the surface in typically both directions normal to the electrode. A condition which must be satisfied for the generation of a piezoelectrically coupled Rayleigh wave is that the crystal axis must be chosen so that two orthogonal elec tric field components E,- under the grid couple to piezoelectric moduli d,-,- which generates the relevant shear and'compressional strain components.

It is thus an object of the present invention to provide an acoustic surface wave preselector utilizing a plurality of interdigital-grids. It is a further object'of the present invention to provide a surface wave preselector which is capable of use in integrated circuits for signal processing applications such as in radio communica tion devices, television tuners, multiplexers, and the like.

SUMMARY OF THE INVENTION Generally, the surface wave preselector of the present invention comprises a base member capable of propagating a surface wave. Preferably, the base comprises a piezoelectric material such as LiNbO Bi GeO SiO GaAs, ZnO, ZnS, CdS and the like formed as a thin-film on a passive substrate.

A first array of interdigital transmitter grids is deposited on the surface of the base member. Each grid comprises 2 sets of N electrodes arranged in a comb configuration from common electrodes. The two sets of elec- 'trodes are interdigitated to form an interdigital grid.

The first array of interdigital grids are utilized to receive an alternating electrical input signal and generate a number of surface waves. The number of grids is determined by the number of channels desired in the preselector as well as by the desired bandwidths of each of the channels. The bandwidth, in part, is dependent upon the number of electrode pairs in each of the interdigital grids. The number of electrode pairs in each grid, on the other hand, is generally determined-by conversion efficiencies. For example, in LiNbO N=l0 provides maximum conversion efficiency. For lO N l7, each electrode pair declines by about 2 dB.

Each of the interdigital grids of the first array is connected to a source of alternating electrical energy, such as an antenna, through a pair of bus lines. The common electrodes of each grid are connected to the bus lines so that all of the grids are connected in parallel. Each grid of the first array is designed to generate a surface wave of a selected frequency and bandwidth in re sponse to a signal having the same frequency.

A second array of interdigital receiver grids is positioned opposite to the first array on the base. Each of the grids of the second array is adapted to receive generated surface waves of selected frequency and bandwidth. The number of grids in the second array is determined by the, frequency and bandwidth of each of the desired channels. It is necessary, however, to position a receiving grid of the second array opposite to a trans-- mitting grid of the first array from which the desired frequencies are transmitted.

Thus, an input signal having a broad band can be broken down into any number of narrower bands. Each transmitting grid is receptive to a specific bandwidth frequency of the input signal and in response to that signal generates a surface wave which is in whole or in part received by an oppositely positioned receiving grid. The signal received by a grid of the second array is then processed in any desired manner.

In an interdigital grid having electrodes of uniform length, the frequency response of each electrode is sin x/x. The bandwidth of each'interdigital gridmeasured between the first zero points from the center frequency is equal to J} if,,/N where N is the number of electrode pairs in each interdigital grid. In a preselector of the present invention, having preferably a number of chansuccessive pairs of electrodes. For example, the electrodes with the widest spacing respond to the lowest input frequency while those with the closest spacing respond to the highest frequency input. The receiver grid is positioned opposite the corresponding transmitter grid so that widest spaced electrodes are nearest the V closest spaced electrodes of the transmitter grid or vice versa. Thus, the distance between corresponding pairs of electrodes in the receiver and transmitter grids is the 'same for all frequencies. The travel time from one grid tothe other is the same for all frequencies which provides a nondispersive preselector device.

Other'advantages of the invention will become apparent from a perusal of the following detailed description of presently preferred embodiments, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FlG. 1 isa block diagram showing a use of the preselector in a radio communication device;

FlG.. 2 is a plan view'of a ten channel preselector according to the present invention;

. FIG. 3 is an enlarged view of the electrodes and spacing of an interdigitalgrid; and

FIG. 4 is' an enlarged 'view of a transmitter and receiver' grid having electrodes therebetween.

" PREVYSENTLY PREFERRED EMBODIMENTS The preselector shown in FlG. 1 is for use in a communications receiver operating in the 30 to 80 MHz with varying spacing band. The description of the preselector in a communications receiver of the specific frequency range is illustrative of one'particular use. It is,however, understood thatthe surface wave preselector of the present invention is adaptable to any number of different frequency ranges, any number of desired channels as well as for use in different applications.

Communication receiver 9 of F IG. 1 includes a surface wave preselector 10 connected to a'receiver an-. tenna 11 and a first mixer 12 to which a first local oscillator13 is connected. First mixer 12 is connected to first lF stage circuit 14, for example, MHz. First lF stage circuit 14 is c'onnected'to a second mixer 16 which has connected thereto a second local oscillator 17'. Second mixer 16 is connected to second lF stage circuit l8 of 25 KHz. ln communication receiver 9, the minimum requirement for preselector is rejection of the image frequency at first mixer 12'. That is, the preselector band pass should be lses than twice, the first immediate frequency, viz., less than 10 MHz.

Since the frequency response of an interdigital grid with electrodes of uniform length is sin x/x, the'bandwidth of the first zero points from center frequency f is f, :f,,/N,.where N is the number of electrode pairs 4 p in the interdigital grid. Thus, a communication receiver 9-as'shown inFlG. 1 could be designed to have ten bands or channels each of which is :5 MHzwide. However, since the fractional bandwidth varies from the lowest to the highest frequency, a different number N of electrode pairs are needed for each interdigital receiver grid center frequency. Utilization of such a design necessitates individually cutting each grid for the photoresist mask. While this is-a suitable method of making a usefulpresel'ector, it involves considerably more expense bandwidth method.

It is preferable to utilize transmitter and receiver I grids in which, a fixed fractional bandwidth is maintained for all channels, but in which the center frequencies of those channels are unevenly spaced. To maintain the requiredoverlap, the zero values of each channel coincides with the maxima of the adjacent channels. Thus, referring to FIG. 2, preselector 10 utilizes fixed fractional bandwidths for each channel. it has been found that for lithium niobate the power gain for a y-cut z-propagation reaches a maximum for l0 elec- I trode pairs and thereafter declines where N is greater than 10 but less than 17 by approximately 2 dB. Ac-

cordingly, preselector 10 in which a lithium niobate surface 20' is used, ten electrodepairs' per interdigital grid achieve-the maximum conversion efficiency. By theutilization of ten electrode pairs, the bandwidth of each of the tenchannels would be i 10 percent.

More particularly, preselector 1,0 includes a first array of interdigital electrode grids 21 deposited on piezoelectric base 20, preferably of LiNbO First array 2l'consists of five interdigital electrode grids 22a-26 as shown in FIG. 3. Electrode grids 22-26 each include five pairs of interdigitated electrodes having common electrodes 22a and 12 ...'26a and b. First array 21 includes a pair of bus lines 28 and'29 to which antenna 11 leads are connected. Grids 22-26 are preferably positioned between bus lines 28 and 29 with the interdigital electrodes positioned substantially parallel thereto. Common electrodes 22a..'.26a are electrically connected to bus line 28 and electrodes 22b...26b are electrically connected tobus line 29.

interdigital electrode grids 22-26 of the first array transmit or generate surface waves upon receiving a signal impressed on antenna 11. in a receiver 9 of FIG.

1, for example, designed for operation in-the 30m 80. MHz band, each grid has a 20 percent bandwidth. ln Table l below, the center frequencies of each transmitting grid-22-26 is set forth together withthe bandwidth and passband. 1 I I TABLE-l f,, BW Passband ID. Grid MHz i MHz MHz r Table ll below sets forth the relevant dimensions for the interdigital transmitter grids 22-26. Referring to preselector for use in than the fixedfractional bodiment w=s, and the aperture width between interdigital grids is fixed at l)\.

TABLE II Transmitter Grid Electrode wimhs from the two original rubyliths for the intermediate and Spucings rubyhth which 1s reduced 100 times. Grid Ml lz X llF'cm V 0 Transmitter Grid spacings. Lengths, 2 5 74 16.85 and RCdUCllOn FZICIUI'S 25 62.0 55) 3.75 1",, W=F)\/4 Reduction Grid length after 26 7M) 4 1 H5 MHz X l()"'cm factor reduction, cm

. 32.5 20.10 4.85 4.97 41.0 20.70 0.12 3.93 A second array 31 of interdigital electrode grids, as 5 -5 6- 7.52 .20 shown in FIG. 3, is deposited on base 20. Second array 31 comprises ten interdigital receiver grids 32-41. Adi jacent receiver grids are positioned on opposite sides of a corresponding transmitter grid. In this embodiment, TABLE W the center frequency of each of the transmitter grids 22-26 is selected to be midway between the center frequencies of two adjacent receiver grids 32-41. This is g fg gfi iggf '"s tfg done to maintain a constant or fixed fractional bandf,, w=s=)\/4 Reduction Grid length after width. Table III discloses the center frequencies of each MHZ X 04cm of the receiver grids 32-41. 3] 27.40 010 TABLE 33 3:28 213% 31.1 43 19.75 0.40 7.72

Center Frequencies of Receiver Grids Passhund 59 14:40 8:75 5:05 MHZ MHZ MHZ 05 1305 9.72 5.10 a a 72 11.30 10.75 4.00 2 if ig? 110 10.00 12.00 4.14 34 39 3.9 3443 43 4.3 39-47 v g 13-23 After. reduction, the master negative mask is used to g 3;, 5:1; 53:65 35 produce a submaster positive mask by contact printing. 39 05 0.5 59-715 1: Q In another embodiment, the bandwidth can be efficiently increased by varying the spacing between successive pairs of electrodes. In FIG. 4, a transmitter grid Table IV below, with reference to FIG. 3, sets forth 60 is positioned on a substrate 61 with a corresponding the relevant receiver grid spacing and electrode widths. receiver grid 62 positioned opposite thereto. The spacing between and the widths of the electrodes for 21 TABLE W square passband are determined in accordance with the following formula: Grid Receiver Grt 'd Electrode wrdthskand Spacmg* W=FM4 Wm /4 l/f l )8f) MHZ where w,, the width of an electrode or space;

v surface wave velocity; 3; :31 2 1 so 6f= Af/3N,-

43 791i) T9175 Af: bandwldth; 36 4g 7L9 1715 f lowest frequency of the band; 37 53 1600 m 1,3,5...3N for electrodes 3s 59 57.0 14.40 65 13.05 m 2,4,6...(3Nl) for spaces, and 40 72 4742 11-80 N total number of electrode pairs.

who The highest frequency electrode 63 of receiver grid Using the measured surface velocit \nlue 11l'\',,= 3.4 X lll cnt sec "I is POSitlOned PP IIE to lowest frequency electrode 64 of transmitter grid 60. Alternatively, the lowest fre- Each interdigital grid 32-41 of second array 31 inquency electrode of the receiver could be positioned cludes a pairof common electrodes 32a and b 41a opposite to the highest frequency transmitter electrode and b to which output leads 42-51 respectively are which would be the case in an arrangement such as connected for connection with a further signal processshown in FIG. 2 where two rows of receiver grids are ing device (not shown). used. Thus, the distance between corresponding elec- By utilizing the preferred embodiment, only two trodes in grids 60 and 62 is the same for all frequencies rubyliths are required, one for the transmitter grids and and the travel time from one grid to the other is the one for the receiver grids, which are reduced by varying amounts from between 4 and 12 to prepare 15 different reduced rubylith grids. The reductions are made as set forth in Tables V and VI below, and then further reduced times to prepare the required photoresist rnask. Tables V and VI show the transmitter and receiver grid dimensions and the reduction factors same for all frequencies.

While presently preferred embodiments have been shown and described in detail, the invention may otherwise be embodied within the scope of the appended c. a second array of interdigital receiver grids deposclaims. ited on said base, the number of said receiver grids What is claimed is: being greater than the number of transmitter grids, l. A surface wave preselector comprising: each of said receiver grids including a pluralityof a, piezoelectric base; parallel electrodes adapted to receive a surface b. a plurality of interdigital transmitter grids deposwave f l d frequency nd b d id h d ited on said base, each of said grids adapted to rebd an output i l at l s n f id Ceive an input Signal and generate a Surface Wave ceiver grids being adapted to receive a surface e p to a Salected frequency of Said input wave of a frequency associated with at least one of 512m]; 10 said transmitter grids and having a bandwidth less a phfrahtypf mterdlgllal f E deposlted than said associated transmitter grid, said associ-j onsard base, each of said grids being adapted to reated grids o Said first and second arrays being ceive a surface wave of selected frequency transposing), positioned on Said base, Said electrodes of mitted' in said base by a transmitter grid and produce an output signal in response thereto, each of said receiver grids being positioned opposite from an associated transmitter grid, and wherein said transmitter and receiver grids each includes a pluw,, v/4 (l/f, +(m-l) 8f),

' rality of electrodes having widths and spaces therebetween in accordance with the following general each of said transmitter and receiver grids having with the following general formula:

where I w the electrode width or space;

widths and spaces, therebet'ween in accordance formula f f/ m v/4 (l/f, (m-l) 8f), Af= the bandwidth; 7 f tlht; lpwgfi bandhfrequency: d h

m= orteeectroewits;

53" gigs l g width or Space m 2,4,6...(3N-l) for the spaces between elec- Af= the bandwidth; trodes; and

' fl the lowest b frequency; N total electrode pairs. v I I m 1 3 5 3 f the electrode widths; 3. A surface wave preselector as set forth in claim 2 m 2 4 3 1 for the Spaces between elec, wherein said second array includes a first andsecond 34 d set of receiver grids, each of said first and second sets N total electrode pairs. comprising the same number of receiver grids as trans- 2. A surface wav preselecmr i i mitter grids, said receiver grids of said first and second a, a piezoelectric b b sets being positioned on opposite sidesof frequency asl y b. a first array'of interdigital transmitter grids depos- 3 5 flled ransmitter grids.

Red on said base, each of said grids being con- 4. A surface wave preselector as set forth in claim 3 nected to an input signal and having a plurality of wherein the center frequency of each of said -transmiti parallel electrodes adapted to generate surface ter grids is selectedgto be midway between the center waves in said base of a selected frequency and frequencies of said associated receiver grids positioned bandwidth in response to an input-signal having 40 on opposite sides thereof. said frequencies; and v v v 

1. A surface wave preselector comprising: a. piezoelectric base; b. a plurality of interdigital transmitter grids deposited on said base, each of said grids adapted to receive an input signal and generate a surface wave in response to a selected frequency of said input signal; c. a plurality of interdigital receiver grids deposited on said base, each of said grids being adapted to receive a surface wave of selected frequency transmitted in said base by a transmitter grid and produce an output signal in response thereto, each of said receiver grids being positioned opposite from an associated transmitter grid, and wherein said transmitter and receiver grids each includes a plurality of electrodes having widths and spaces therebetween in accordance with the following general formula? wm v/4 (1/f1 + (m-1) delta f), where wm the electrode width or space; delta f Delta f/3N; Delta f the bandwidth; f1 the lowest band frequency; m 1,3,5...3N for the electrode widths; m 2,4,6...(3N-1) for the spaces between electrodes; and N total electrode pairs.
 2. A surface wave preselector comprising: a. a piezoelectric base member; b. a first array of interdigital transmitter grids deposited on said base, each of said grids being connected to an input signal and having a plurality of parallel electrodes adapted to generate surface waves in said base of a selected frequency and bandwidth in response to an input signal having said frequencies; and c. a second array of interdigital receiver grids deposited on said base, the number of said receiver grids being greater than the number of transmitter grids, each of said receiver grids including a plurality of parallel electrodes adapted to receive a surface wave of selected frequency and bandwidth and produce an output signal, at least one of said receiver grids being adapted to receive a surface wave of a frequency associated with at least one of said transmitter grids and having a bandwidth less than said associated transmitter grid, said associated grids of said first and second arrays being opposingly positioned on said base, said electrodes of each of said transmitter and receiver grids having widths and spaces therebetween in accordance with the following general formula: wm v/4 (1/f1 + (m-1) delta f), where wm the electrode width or space; delta f Delta f/3N; Delta f the bandwidth; f1 the lowest band frequency; m 1,3,5...3N for the electrode widths; m 2,4,6...(3N-1) for the spaces between electrodes; and N total electrode pairS.
 3. A surface wave preselector as set forth in claim 2 wherein said second array includes a first and second set of receiver grids, each of said first and second sets comprising the same number of receiver grids as transmitter grids, said receiver grids of said first and second sets being positioned on opposite sides of frequency associated transmitter grids.
 4. A surface wave preselector as set forth in claim 3 wherein the center frequency of each of said transmitter grids is selected to be midway between the center frequencies of said associated receiver grids positioned on opposite sides thereof. 